Harden SkPerlinNoiseShader StitchData initialization

... to ensure fWrap{X,Y} don't overflow int.

Bug: chromium:846010, oss-fuzz:8377
Change-Id: I7cf082e388002ad5f8a6c62bad92f998fe831385
Reviewed-on: https://skia-review.googlesource.com/132222
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Florin Malita <fmalita@chromium.org>
1 file changed